film is made in more than one layer. some has 2 layer some 3.......Another issue is what type of glue. some is a PS or pressure sensitive and some are a CDF or dry adhesive. PS is sticky like tape, adheres more quickly and generally dries faster, this is the film installed on automotive. CDF is tacky and is used more for rezi and comercial, Although some comercial films use a PS adhesive such as White Matte and Blackout ect. CDF is designed so that when working with large pieces and the film touches together it does not get ruined. PS films are designed more to be shrunk and fit on cars. PS is usually easier to remove after cured. CDF can be difficult to remove although it has a longer cure time, after curing it sticks really well. This is my experience opinions vary.
best way to remove film is to get water to the glue. one way is steam. one way is spraying water on film and bagging it. Another less popular idea.....if the film is acting like you say "not peeling clean" you can install a new layer of cheap film over the top of the old crusty stuff then let it set in the sun for a while then peel. this should soften the glue under the old film. Either way make sure to get all the layers on the first peel.
anyone interested in film can search the tintdude forum. I am also a regular forum user there.
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